Technology has been proposed to transmit an electric potential difference between electrodes coupled by using the human body as a part of a transmission path. According to this technology, for example, a transceiver and a receiver, each having two electrodes, have been used. One of the electrodes is a signal electrode connected to a signal line, and the other is a ground reference electrode connected to a ground having a reference potential. To transmit an electric potential difference between the signal electrode and the ground reference electrode, the signal electrodes of the transmitter and the receiver are coupled mainly via the human body, and the ground reference electrodes are coupled mainly via the air or the land and transmit the reference potential.
With this structure, noise from another system or an electric potential fluctuation of a signal transmitted on the human body affects the reference potential. Such an electric potential fluctuation is caused by a coupling with the human body near the transceiver and the receiver. The instability caused by the electric potential fluctuation causes low communication quality.